1. Field of the Invention
The present invention relates to a circuit breaker, and particularly, though not exclusively, to an automatic cut-out or line-protective circuit breaker, which includes a housing, an electric arc chamber arranged within the housing, a fixed contact and a movable contact located in the arc chamber, a current supply line forming a U-shaped current loop with the contacts. The arc-extinguishing chamber incorporates arc-extinguishing plates for guiding the path of the arc into the electric arc chamber to the extinguishing chamber, and in which plates of a magnetically-conductive material extend in parallel with the plane of contact movement up to opening or breaking thereof, and extend from the contacts to the arc-extinguishing chamber, and a gas-emitting coating being provided on each of the plates and constituted of an electrically-insulating material which emits gas when heated.
Circuit breakers of that type are generally known, for example, from German Laid-open Patent Application No. 30 30 429. In accordance therewith, in the usual manner for the guidance of the electric arc into an extinguishing chamber which is, in particular, equipped with extinguishing plates, there is obtained an electric arc guide aid in which the stationary contact and the movable contact, in conjunction with the current supply line, form a U-shaped current loop, and wherein plates of a magnetically conductive material embedded in electrically-insulating material are arranged to extend in parallel with the plane of the contact movement; for example, as is already known from German Published Patent Application No. 10 12 662 and German Patent Specification No. 480,802. In electric arc path guide aids of that type it is possible to provide a construction without the need for the additional blowout coils which were frequently employed up to that time; for instance, as in German Patent Specification No. 480802. The plates for the electric arc path guide aids are suitably provided with a coating of an electrically-insulating material, as disclosed in German Published Patent Application Nos. 10 61 866 and 10 12 662, and German Patent Application No. 914 869. Herein, it is also known that for circuit breakers with electric arc path guide aids, there could be employed a material which is gas-emitting when subjected to heat, as disclosed in German Patent Specification Nos. 914869; 11 85 274 and 280,663. Usually, guide plates are employed for the electric arc, which are frequently formed of an insulating material, which extend from the contacts to the extinguishing chamber within which there are arranged, as a rule, extinguishing plates. A construction of that type is evidenced in many of the circuit breakers which are currently being marketed.
The development of circuit breakers has led in the direction of always higher nominal or rated current intensities, a broadening of the range for instantaneous actuation, and leading to always higher switching capabilities at lower output losses and lower heat transmission values, or in other words; in the direction of a lower power conversion at the smallest dimensions and lower manufacturing costs.
The higher rated current intensities and the broadening of the range for the instantaneous actuation provide the result that the contacts must open or break at always higher current levels. Notwithstanding the usual magnetic quick-release switches with impact action on the movable contact and with electric arc drive through a blowout coil, which form the current infeed and the contacts, pursuant to current technological developments it is difficult to drive the electric arc sufficiently rapidly into the extinguishing chamber.